1. Field of the Invention
This invention relates to ceramic-metal composite bodies.
2. Related Art Statement
As shown in FIG. 3, the conventional ceramic-metal composite body has hitherto been produced by fitting a protruding portion 22 of a ceramic member 21 into a concave portion 24 of a metallic member 23 through press fitting, shrinkage fitting, contraction fitting or the like.
In general, it is known that the fatigue of the metallic member frequently occurs and grows from the metal surface and also the life until fatigue failure becomes shorter as the stress produced in the metallic member is large. In the ceramic-metal composite body having such a structure that the protruding portion of the ceramic member is fitted into the concave portion or through-hole formed in the metallic member through press fitting, shrinkage fitting, contraction fitting or the like, the tensile stress always acts to the metallic member at the fitted portion between both members. Particularly, if undulation is existent in the protruding portion of the ceramic member, a larger tensile stress is locally caused in the concave portion of the metallic member, which is apt to easily cause fatigue failure.
In the conventional ceramic-metal composite body, therefore, considerable stress concentration is caused due to the undulation in a plane including the axial line of the protruding portion 22 of the ceramic member 21, at a peak of the undulation, particularly a peak existent in the fitted end of the protruding portion 22. As a result, the resistance to bending or torsion is weak, resulting in the failure of the composite body, so that the ceramic-metal composite body having a high reliability can not be obtained.